Numberical simulation of the effects of radially injected barium plasma in the ionosphere

The morphology of the ion cloud in the radial shaped charge barium injection was studied. The shape of the ion cloud that remains after the explosive products and neutral barium clears away was examined. The ion cloud which has the configuration of a rimless wagon wheel is shown. The major features are the 2.5 km radius black hole in the center of the cloud, the surrounding ring of barium ion and the spokes of barium ionization radiating away from the center. The cloud shows no evolution after it emerges from the neutral debris and it is concluded that it is formed within 5 seconds of the event. A numerical model is used to calculate the motion of ions and electrons subject to the electrostatic and lorenz forces

Scaling forces to asteroid surfaces: The role of cohesion

The scaling of physical forces to the extremely low ambient gravitational acceleration regimes found on the surfaces of small asteroids is performed. Resulting from this, it is found that van der Waals cohesive forces between regolith grains on asteroid surfaces should be a dominant force and compete with particle weights and be greater, in general, than electrostatic and solar radiation pressure forces. Based on this scaling, we interpret previous experiments performed on cohesive powders in the terrestrial environment as being relevant for the understanding of processes on asteroid surfaces. The implications of these terrestrial experiments for interpreting observations of asteroid surfaces and macro-porosity are considered, and yield interpretations that differ from previously assumed processes for these environments. Based on this understanding, we propose a new model for the end state of small, rapidly rotating asteroids which allows them to be comprised of relatively fine regolith grains held together by van der Waals cohesive forces.Comment: 54 pages, 7 figure

Knickzones in Southwest Pennsylvania Streams Indicate Accelerated Pleistocene Landscape Evolution

A set of 22 southwestern Pennsylvania streams flowing into the Monongahela and Ohio rivers with drainage areas ranging from 8 km2 to \u3e512 km2 exhibit knickzones, when compared to Mackin’s (1948) idealized graded stream profile. Watersheds delineated from LiDAR-derived 1 m DEMs were processed using Esri’s ArcGIS for Desktop 10.6 to extract stream elevation data used to create stream profiles. These data were exported to MS Excel, where gradients were calculated and compared. This study used a new methodology in which gradient was calculated using incremental measurement distances (d) at every meter along the length of each stream. Profile convexities were identified where downstream reach (d/2d) gradient was greater than upstream reach (d/2u) gradient, and “knickzone extents” were designated where extended stream reaches had downstream gradients ≥.001 and ratios of downstream to upstream reach gradients ≥1.2. A selection of stream profiles was plotted using Goldrick and Bishop’s (2007) DS profile form, revealing most upper reaches fit the graded stream model, but lower reaches show disequilibrium steepening. Disequilibrium was likely induced by the rerouting of the regional drainage to its present configuration by Pleistocene glaciation, based on strong correlation of knickzones elevations with elevations of Pre-Illinoian and Illinoian terrace features along the main trunk rivers. The best correlation occurred when study area streams were compared by confluence location along the main trunk, possibly due to the lithologic differences in bedrock across the area or due to differences in the evolution of the Allegheny and Monongahela rivers. Although knickzones were assumed to have migrated into study area tributaries from the main trunk, migration distance appears to be controlled more by lithology or pre-incision topography rather than time elapsed since inducement of disequilibrium

Investigation of metal mediated reactions for natural product synthesis

During the course of the studies outlined in this thesis, an ether-directed Pd(II)-catalysed aza-Claisen rearrangement reaction that had previously been developed by the Sutherland group was expanded to include more functionalised rearrangement substrates. This methodology has been applied for the synthesis of several natural products including dihydroxylated-amino acids. Further investigation of substrates for the rearrangement led to the synthesis of other substituted trichloroacetimidates. Rearrangement of these compounds demonstrated the role of steric strain on the stereocontrol of the rearrangement and also highlighted the role that solvent can have upon the diastereoselectivity of ether-directed rearrangements. In addition to this, a novel tandem aza-Claisen rearrangement and ring closing metathesis reaction has been developed. This reaction allows the synthesis of cyclic allylic trichloroacetamides in excellent yields from simple allylic alcohols. The use of commercially available chiral rearrangement catalysts allowed a highly enantioselective tandem process to be developed. Further development of this process has provided an ether-directed tandem aza-Claisen rearrangement and RCM reaction which occurs with high yield and diastereoselectivity to provide functionalised cyclic products. The use of these compounds for the total synthesis of the amaryllidaceae alkaloid (+)-gamma-lycorane was also investigated